sustainability Article Human-Induced Enrichment of Potentially Toxic Elements in a Sediment Core of Lake Balkhash, the Largest Lake in Central Asia Kun Huang 1,2,3, Long Ma 1,2,3,* , Jilili Abuduwaili 1,2,3 , Wen Liu 1,2,3 , Gulnura Issanova 2,4, Galymzhan Saparov 2,5 and Lin Lin 6 1 State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China; [email protected] (K.H.); [email protected] (J.A.); [email protected] (W.L.) 2 Research Center for Ecology and Environment of Central Asia, Chinese Academy of Sciences, Urumqi 830011, China; [email protected] (G.I.); [email protected] (G.S.) 3 University of Chinese Academy of Sciences, Beijing 10049, China 4 Faculty of Geography and Environmental Sciences, Al-Farabi Kazakh National University, Almaty 050040, Kazakhstan 5 Kazakh Research Institute of Soil Science and Agrochemistry Named after U. U. Uspanov, Almaty 050060, Kazakhstan 6 Water Research Institute of Shandong Province, Jinan 250014, Shandong, China; [email protected] * Correspondence: [email protected]; Tel.: +86-991-782-7371 Received: 22 May 2020; Accepted: 8 June 2020; Published: 9 June 2020 Abstract: Over the past century, the impacts of human activities on the natural environment have continued to increase. Historic evolution of the environment under anthropogenic influences is an important reference for sustainable social development. Based on the geochemical analyses of a short sediment core of 49 cm from Lake Balkhash, the largest lake in Central Asia, potential factors historically influencing geochemical variation were revealed, and influences of human activity on regional environmental change were reconstructed over the past 150 years. The results showed that the dominant factor inducing changes in potentially toxic elements (V, Cr, Co, Ni, Zn, Cu, Cd, and Pb) is the physical weathering of the terrestrial materials. The variation in Ca content was influenced by the formation of authigenic carbonate. Since 1930, potentially toxic elements (Cr, Co, Ni, Zn, Cu, Cd, and Pb) in the lake sediments have obviously been affected by human activities, but the impact of human activities has not exceeded that of natural terrestrial weathering. In particular, the enrichment factors (EFs) for Cd and Pb reached 1.5. The average ecological risks of Cd were higher than the criterion of 30, suggesting a moderate risk to the local ecosystem in recent years. Total risk indices indicated moderate potential ecological risk for the lake ecology. The results will provide support for the environmental protection and better management practices of the Lake Balkhash watershed. Keywords: human activity; enrichment factors; potentially toxic elements; Lake Balkhash; Central Asia 1. Introduction As element composition in lake sediments is generally derived from weathered rock, eroded soil, and anthropogenic inputs, it has been widely used to study environmental change for the reconstruction of human impacts [1–4]. Over the past century, the impacts of human activities on the natural environment have continued to increase [5,6]. With the promotion of modernization since the industrial revolution, element profiles in sediments have been affected not only by natural processes Sustainability 2020, 12, 4717; doi:10.3390/su12114717 www.mdpi.com/journal/sustainability Sustainability 2020, 12, 4717 2 of 13 but also by human activities [7]. Hence, further study of the geochemistry of elements in lake sediments is needed to better understand the evolution of the physical geographical environment under the influence of human activities [8,9]. Meanwhile, the enrichment and contamination of potentially toxic elements in the natural environment have been receiving more and more attention due to the biological toxicity and environmental persistence of these elements [10]. As the largest inland lake in Central Asia, Lake Balkhash plays an important role in maintaining ecological equilibrium across the region. Unfortunately, Lake Balkhash is vulnerable to anthropogenic disturbances due to its shallowness, relatively fragile ecosystems, and proximity to metallurgical industries [4]. Ever since intensive agricultural development began following the settlement of the Russian population in the late 19th century [11], the chemical and physical characteristics of Lake Balkhash have undergone obvious changes; for example, there has been a considerable increase in the lake’s salt content since the second half of the 20th century [12], and pollutants containing potentially toxic elements and oil products have appeared [11]. In addition, a dramatic decrease in the lake’s water level following the filling of the Kapchagay Reservoir in the 1970s aroused worldwide concern that Lake Balkhash would face the same fate as the Aral Sea [13]. Scientific research is necessary for the protection and sustainable development of Lake Balkhash. Studies have been carried out on the changing lake dynamics [14–16], regional climate [17], and aquatic ecology [18,19]. However, the environmental responses of Lake Balkhash to the increasing human activity in the region are not yet well understood. Furthermore, previous studies on the sediments of Bosten Lake [20], Ebinur Lake [21], and Chaiowpu Lake [22] have indicated what influence human activities have had on other arid regions of China adjacent to Lake Balkhash with similar natural conditions; however, spatial differences in the response to global change still need to be explored. This paper focused on the scientific hypothesis of whether the potentially toxic elements in the sediments of Lake Balkhash are enriched by human activities over time, and different from those in the adjacent area under the background of significant enhancement of human activities. With the geochemical composition of Lake Balkhash’s sediments, this study aims to identify element sources and to reconstruct the influences of human activities on regional environmental change. In turn, this will provide support for the environmental protection of Lake Balkhash and the application of better management practices to the watershed. 2. Regional Setting The Ili–Balkhash Basin (IBB) covers 4.1 105 km2, and the Kazakh part of the basin contains × one-fifth of that country’s total population [23] (Figure1). The multiyear mean temperature and precipitation in the basin range from 3.1–9.2 ◦C and 124–633 mm, respectively [17]. In the north, the IBB is dominated by grassland, and the Saryesik–Atyrau desert lies to the south of the lake. Forest prevails southeast of the IBB, and the arable land is mainly distributed along rivers. The rapid economic development in this region benefited from the construction of the railroad and the rise of the nonferrous metal industry in the 1930s [11]. Irrigation land for agriculture expanded from an area of 3520 km2 in 1955 to 5596 km2 in 1984. Consequently, water shortages and pollutant emissions in conjunction with population growth and economic development had an adverse impact on the ecosystem of Lake Balkhash [11,24]. The surface are of Lake Balkhash (44◦480–48◦490 N, 73◦300–79◦160 E) is variable and generally ranges from 17,000 to 22,000 km2 [25]. Lake Balkhash is divided into two relatively independent parts. The western part is shallower with an average depth of 7–11 m and less mineralized due to the influence of the Ili River (supplying 78% of the total riverine runoff) that flows into it. An extensive delta is formed where the river flows into the lake, which naturally regulates ecological and water balance within the Ili–Lake Balkhash system [26]. Other rivers such as the Karatal, Aksu, Lepsy, and Ayaguz terminate in the eastern part of Lake Balkhash. Mineralization in the southwestern basin is 1 1 1.85 g L− , whereas in the eastern basin it is 4.58 g L− [12]. Based on our analysis, water of Lake Balkhash belongs to the sulfate class with the sodium group [12]. The climate in the area of the lake Sustainability 2020, 12, 4717 3 of 13 Sustainability 2020, 12, x FOR PEER REVIEW 3 of 13 is continental, with low annual precipitation (150 mm) but intense evaporation (1000 mm), and an 96 annualis continental, mean temperature with low annual of 6 ◦C[ precipitation27]. (150 mm) but intense evaporation (1000 mm), and an 97 annual mean temperature of 6 °C [27]. 98 99 FigureFigure 1. 1.Location Location ofof LakeLake BalkhashBalkhash in Central Asia (A), (A), and location location of of the the sampling sampling site site in in Lake Lake 100 BalkhashBalkhash (B (B).). 101 3.3. Materials Materials and and Methods Methods 3.1. Sampling and Laboratory Analyses 102 3.1. Sampling and Laboratory Analyses A 49 cm long sediment core was extracted in 2017 from the sampling site (45 41 5.2 N, 103 A 49 cm long sediment core was extracted in 2017 from the sampling site (45°41◦ ′5.20 ′’ 00N, 73 45 5.5 E) in Lake Balkhash using a piston–percussion corer fitted with 60 mm internal diameter 104 73°45◦ 0 ′5.500′’ E) in Lake Balkhash using a piston–percussion corer fitted with 60 mm internal diameter 105 PerspexPerspex tubes tubes (Figure (Figure1 ).1). The The sediment sediment corecore waswas slicedsliced inin situsitu into thin horizontal sections sections at at 1 1 cm cm 106 intervalsintervals using using a a plastic plastic cutter. cutter. Forty-nine Forty-nine (49) (49) sediment sediment samples samples were were obtained obtained and and dried dried at at –50 –50◦ C°C in 107 ain continuous a continuous vacuum vacuum freeze dryerfreeze fordryer subsequent for subsequent dating and dating geochemical and geochemical analysis. The analysis. freeze-dried The 137 108 samplesfreeze-dried were samples homogenized were homogenized and weighed, and and weighed, then analyzed and then for analyzedCs by direct for 137Cs gamma by direct spectrometry gamma 109 usingspectrometry an Ortec HPGeusing GWLan Ortec series HPGe well-type, GWL coaxialseries lowwell-type, background coaxial intrinsic low background germanium intrinsic detector 110 (EG&Ggermanium ORTEC, detector Oak (EG&G Ridge, ORTEC, TN, USA) Oak [28 Ridge,].